The proposed research is designed to test the efficacy of carbamazepine in delaying or preventing decompensation during neuroleptic drug-free periods in 68 outpatients suffering from psychotic illnesses--either schizophrenia or schizoaffective illness. It consists of a double-blind crossover, controlled trial of carbamazepine vs. placebo. Involving sequential 4-month treatment phases over an overall experimental treatment course of 34 weeks, the study has both a general and specific focus. The former considers the prophylactic efficacy of carbamazepine with a broad range of patients with schizophrenic features who have been diagnosed as schizophrenic or schizoaffective by the Research Diagnostic Criteria. The narrower focus is on patterns associated with treatment success/failure, including evidence of episodic dyscontrol. For present purposes, this evidence is based on the results of the Monroe Scale, a self-report questionnaire that identifies behaviors and experiences common to episodic dyscontrol. Theoretical considerations, as well as anecdotal experience and the results of open and controlled clinical trials, suggest that this type of patient is especially likely to benefit from treatment with carbamazepine. Outcome measures will be of two types: decompensation versus no decompensation and length of time to decompensation in placebo and carbamazepine conditions. The level and type of psychopathology will also be examined with respect to outcome in the two treatment conditions.